A protective device of the type mentioned above is known from U.S. Pat. No. 6,494,134 as a component of a foil stencil assembly. The foil stencil assembly comprises a foil stencil secured to a rigid frame in a planar configuration. The rigid frame has an upright side wall and a support flange extending inwardly from the upright side wall. The stencil foil rests on the support flange, and the outer edge of the foil stencil is positioned adjacent to the inner surface of said side wall. The stencil foil is secured along its circumference to the rigid frame. Due to the rigid frame, waviness of the foil stencil can hardly be avoided. The known foil stencil assembly can be mounted onto a stretcher frame so that a printing procedure can be carried out.
Moreover, German patent specification DE 197 49 449 C1 discloses a stencil stretcher frame for stretching stencils made of metal or plastic foils for stencil printing, said stencil stretcher frame having a stretching device for adjustable stretcher bars that can be operated by means of a pressure medium. The stretcher bars have gripping pins that engage with perforations of a stencil. The stretching device is made up of elastically deformable stretcher tubes that are arranged in a frame section, that can be uniformly charged with a pressure medium and on which the stretcher bars lie on the front. Moreover, the stretcher bars are provided at the rear with pivoting cams that rest on an end section of the frame section, namely, in such a way that the stretcher bars can be pivoted on the pivoting cams by means of the stretcher tubes in order to stretch the stencil. With this stencil stretcher frame, a stretching force can be applied uniformly onto the entire working surface of the stencil. In this manner, waviness of the stencil is avoided. In the known stencil stretcher frames, the stencil made of a metal or plastic foil has to be laid in place loosely by hand.